Fast hardware simulation engines are a recent development in response to the increasing complexity of very large scale integrated (VLSI) circuits, ad provides a much more rapid simulation than the more conventional software packages.
Present hardware simulation engines have a digital modelling scheme and simulate the VLSI circuit as a series of time delay switches, the overall time delay of a particular region in the circuit being a progressive summation of the time delay of each circuit element. Circuits using elements such as transistors have a unique transient response which is dependent on its characteristic and the inherent capacitance in and around the transistors. In circuits which rely on the detailed characteristics of transistors, a switch level simulation may produce an incorrect result. Accordingly it would be desirable to simulate the VLSI circuit in order to obtain not only the correct logical result but also the transient response of the circuit.
Present digital hardware simulation engines, due to their digital simulating technique, do not model transient response due to the necessarily high number of variables and the overly long computational time period.
Therefore, digital hardware simulators are ineffective in modelling transient response, especially in the simulation of low level circuits where the transient response must be calculated in order to simulate the circuit correctly.